Csharp .NET 6 PeriodicTimer 具有最先进的计时功能

标准中没有可用的内容.NET库，具有此功能.而且我不认为它很快会被加入.我的建议是使用第三方Cronos库，它可以很好地处理时间间隔的计算.您可以找到斯蒂芬·克利里的用法示例here.这个库只计算时间间隔，不做任何调度.

如果您想获得更多乐趣，可以将Cronos库的功能包含在定制的PeriodicTimer类组件中，如下所示:

using Cronos;

public sealed class CronosPeriodicTimer : IDisposable
{
    private readonly CronExpression _cronExpression;
    private readonly CancellationTokenSource _cts;
    private static readonly TimeSpan _minDelay = TimeSpan.FromMilliseconds(500);

    public CronosPeriodicTimer(string expression, CronFormat format)
    {
        _cronExpression = CronExpression.Parse(expression, format);
        _cts = new();
    }

    public async ValueTask<bool> WaitForNextTickAsync(
        CancellationToken cancellationToken = default)
    {
        if (_cts.IsCancellationRequested) return false;
        CancellationTokenSource linkedCts = null;
        CancellationToken token = _cts.Token;
        if (cancellationToken.CanBeCanceled)
        {
            cancellationToken.ThrowIfCancellationRequested();
            linkedCts = CancellationTokenSource
                .CreateLinkedTokenSource(_cts.Token, cancellationToken);
            token = linkedCts.Token;
        }
        try
        {
            DateTime utcNow = DateTime.UtcNow;
            DateTime? utcNext = _cronExpression.GetNextOccurrence(utcNow + _minDelay);
            if (utcNext is null)
                throw new InvalidOperationException("Unreachable date.");
            TimeSpan delay = utcNext.Value - utcNow;
            Debug.Assert(delay > _minDelay);
            try
            {
                await Task.Delay(delay, token).ConfigureAwait(false);
                return true;
            }
            catch (OperationCanceledException)
            {
                cancellationToken.ThrowIfCancellationRequested();
                return false;
            }
        }
        finally { linkedCts?.Dispose(); }
    }

    public void Dispose() => _cts.Cancel();
}

除了构造函数之外，CronosPeriodicTimer类与PeriodicTimer类具有相同的API.您可以这样使用它:

var timer = new CronosPeriodicTimer("0 * * * * *", CronFormat.IncludeSeconds);
//...
await timer.WaitForNextTickAsync();

表达式0 * * * * *表示"on the 0 (zero) second of every minute, of every hour, of every day of the month, of every month, and of every day of the week."

您可以找到关于Cron表达式here格式的详细文档.

Note:为了处理Task.Delay比目标DateTime完成earlier的场景，WaitForNextTickAsync的延迟至少为500毫秒.我无法通过实验实现这种情况.Task.Delay总是在几毫秒after内完成我机器中的目标DateTime.尽管如此，为了防止计时器两次错误滴答作响的可能性微乎其微，还是应该包括这一安全措施.此功能在实践中不应有任何明显的效果.